1. Field of the Invention
The present invention generally relates to an apparatus and method for transmitting facsimile data and, more particularly, to a facsimile system for transmitting data in real-time over a standard digital data network, or an analog network, whereby the facsimile data is sent in data packets on the digital data network.
2. Discussion of Related Art
In a known facsimile transmission, as shown in FIG. 1(a), a facsimile (fax) machine 10 dials a destination phone number and the call is routed through a central office Local Exchange Carrier LEC CO 14. A connection is made from the LEC Co 14 to an inter-exchange carrier's Point of Presence, IXC POP 16. IXC POP 16 makes a connection through a long distance carrier facility 15, to a destination IXC POP 17, which in turn makes a connection to a destination LEC CO 18. The destination LEC CO 16 then calls the phone number of the destination facsimile machine 11. Once the destination facsimile machine 11 answers, an end-to-end connection is established between the two facsimile machines 10, 11. The appropriate facsimile session setup is then performed by the two facsimile machines 10, 11, and this is followed by the facsimile data transmission. Upon completion of the facsimile transmission, the facsimile machines hang-up and the connection is terminated.
In the known system of FIG. 1(a), when one facsimile machine dials another, a circuit-like connection is created between the two machines. There is very little delay from when the source facsimile machine 10 sends data to when the destination facsimile 11 machine receives the data.
Further in the known system, the telecommunications services (phone lines, etc.) used for typical facsimile transmissions, and their associated cost structure, are formally defined by the carrier in a document called a tariff. Tariffs are filed for approval by state regulatory commissions and/or the Federal Communication Commission (FCC).
Other known systems use store and forward services for facsimile transmission. With store and forward, a facsimile is generally transmitted to a local vendor with information about the final destination. The local vendor then takes responsibility for delivering the facsimile. Such services are not in real-time in that there is no circuit-like connection between the source and destination facsimile machines. In such systems, the facsimile transmission is usually sent at a later time when the rates are less. A disadvantage to this technique is that in the event a facsimile cannot be delivered to the destination facsimile machine, there may be no reliable way of notifying the user of the source facsimile machine that the facsimile has not been delivered. Important facsimiles requiring immediate delivery and confirmation of receipt generally cannot be sent through such systems.
Another conventional way of reducing costs of data transmission including, for example, voice data, is to use alternate communication services, such as dedicated telephone lines such as a Wide Area Telephone Service (WATS) line. Alternatively, telephone companies offer a variety of overlapping discount schedules which could be utilized to minimize costs for a particular transmission. A disadvantage of using such alternate communication services is that a user has to be aware of a multitude of telephone number, access codes, and rate schedules.
Facsimile transmissions today are accomplished through the use of analog grade circuits, also known as POTS (Plain Old Telephone Service). Facsimile transmissions are inherently digital and need to be converted to analog only for compatibility with the existing access methods (i.e. voice grade lines). The bandwidth of analog voice grade circuits is very small and so the telephone companies have migrated most if not all of their equipment to provide transmission services using a digital network. The conversion of analog voice into digital form used in the digital networks involves a fairly high data rate of 64 Kbps, however, facsimile data is transmitted at a much lower data rate of, typically, 9.6 Kbps or 14.4 Kbps. A disadvantage of such systems is that when facsimiles are transmitted over a voice grade circuit through the network's digital transmission facilities, most of the bandwidth of the digital network is not utilized even though it is being paid for.
An example of the above-described digital network is shown in FIG. 1(b), and corresponds to a system recommended in a document published by the ITU. In the ITU system, data is transmitted digitally between a source facsimile packet assembly/disassembly facility (FPAD) 4 and a destination FPAD 6 through a Packet Switched Public Data Network (PSPDN) 5. The access to either FPAD 4 or 6 is still made through its respective General Switched Telephone Network (GSTN) 3 or 7. The ITU system has some technical characteristics; however, which make it unattractive, particularly for facsimile transmissions. They are:
1. It runs on X.25 protocol which significantly increases the length of call. PA1 2. It does not guarantee delivery of data. PA1 3. It has a variable delay in delivery of communicated packets. PA1 4. It does not accommodate switched analog access lines.